1. Field of the Invention
The present invention relates to a plasma display panel using an emission from phosphors excited by vacuum ultraviolet rays generated by a rare gas discharge.
2. Description of the Related Art
As shown in FIG. 9, in an AC plasma display panel, a front substrate 21 and a back substrate 22 are positioned opposing each other with a discharge space 23 interposed therebetween. On the front substrate 21, pairs of stripe-shaped scanning electrodes 26 and sustain electrodes (not shown) are arranged so as to extend in the direction parallel to a paper surface. They are covered with a dielectric layer 24 and a protective layer 25. On the back substrate 22, stripe-shaped data electrodes 27 are arranged in the direction perpendicular to the scanning electrodes 26 and sustain electrodes. Stripe-shaped separation walls 28 are provided between the data electrodes 27 to form discharge cells 29 together with the front substrate 21 and the back substrate 22. Furthermore, phosphors 30 are provided on the data electrodes 27 and side faces of the separation walls 28. Each phosphor 30 is provided on each discharge cell 29 with respect to each color, and thus red, green, and blue phosphors are arranged successively.
In the plasma display panel, the phosphors 30 applied to the display cell are excited by 147 nm-wave length vacuum ultraviolet rays generated by a rare gas discharge. The emitted ray is used for color display. A well known example of materials for the phosphor 30 includes a red phosphor such as an europium activated yttrium, gadolinium borate phosphor, (Y, Gd) BO3: Eu, a green phosphor such as a manganese activated zinc silicate phosphor, Zn2SiO4: Mn, a blue phosphor such as an europium activated barium magnesium aluminate phosphor, BaMgAl10O17: Eu, and the like.
Conventionally, the Zn2SiO4: Mn phosphor that generally has been used for a green phosphor has a surface potential with a negative polarity. FIG. 10 shows a blow-off charging amount of various phosphors. As is shown in FIG. 10, only Zn2SiO4: Mn is charged negatively. It is estimated that variation of discharge characteristics in the plasma display panel is dependent upon this negative charge.
The present inventors have found that when the voltage is applied to a surface of a phosphor using such a phosphor for display, discharge variation or discharge error, i.e., failure of generating discharge, occurs more frequently as compared with the phosphors charged positively. This phenomenon deteriorates the quality of the display, or requires an increase in set driving voltage in order to raise the voltage until complete lighting is obtained so as to maintain the high quality.
The charging amount of the phosphor is a physical property value that is determined depending upon kinds of materials. Therefore, it is difficult to modify this physical property value. One method for modifying the charging amount, suggested in JP 11(1999)-86735A, is that a film for modifying the polarity be laminated on the phosphor layer. However, there are problems in that the number of steps is increased due to laminating a film of non-emitting materials, or luminance is lowered.
Furthermore, an example of green phosphor emitting by excitation by vacuum ultraviolet rays includes manganese activated barium magnesium aluminate, BaAl12O19: Mn phosphor. The surface potential of this phosphor is charged with a positive polarity and the discharge is stable. However, this phosphor has low luminance and is deteriorated significantly over time during the operation of the panel. Thus, this is not suitable for practical use.
Another example of the green phosphor is terbium activated yttrium borate, YBO3: Tb phosphor. This phosphor has the surface potential with a positive polarity, but has the color purity inferior to a copper, gold activated zinc sulfide phosphor, ZnS:Cu, Au (JEDEC registered No. P-22), and the region for reproducing color becomes narrower. Thus, the quality of the display is deteriorated.
It is an object of the present invention to provide a plasma display panel capable of stabilizing the discharge property and realizing a high luminance and long lifetime, and having the same or higher degree of the color purity as compared with that of CRT.
The present inventors have found that the use of a mixed phosphor obtained by mixing a phosphor having a surface potential with a negative polarity and a phosphor having a surface potential with a positive polarity for the phosphor screen makes it possible to stabilize the discharge without deteriorating the luminance.
Therefore, a plasma display panel of the present invention includes plural kinds of phosphor layers emitting different colors of fluorescent light. At least one kind of phosphor layer is formed of a mixed phosphor obtained by mixing a phosphor having a surface potential with a negative polarity and a phosphor having the surface potential with a positive polarity.
With such a configuration, the surface potential of the phosphor is changed from the negative polarity to the positive polarity, so as to reduce the discharge variation or discharge error in the plasma display panel. Thus, it is possible to display a picture stably.
Furthermore, the plasma display panel of the present invention includes a pair substrates positioned opposing each other with a discharge space provided therebetween where at least front substrate is transparent, a separation wall disposed on at least one substrate so as to divide the discharge space into several parts, a group of electrodes arranged on the substrate so that discharge is performed in the discharge spaces divided by the separation walls, and phosphor layers emitting light by the discharge. In the plasma display of the present invention, the phosphor layers include plural kinds of phosphor layers emitting different colors of fluorescent light, at least one kind of the phosphor layer being formed by using a mixed phosphor obtained by mixing a phosphor having a surface potential with a negative polarity and a phosphor having a surface potential with a positive polarity.
In either of the above-mentioned configurations, it is possible to form a mixed green phosphor layer formed of a mixed phosphor obtained by mixing a manganese activated zinc silicate phosphor represented by the general formula, Zn2SiO4: Mn and having a surface potential with a negative polarity and a terbium activated rare earth borate green phosphor represented by the general formula, ReBO3:Tb, wherein Re denotes one rare earth element or a solid solution of plural kinds of rare earth elements selected from the group consisting of Sc, Y, La, Ce and Gd, having a surface potential with a positive polarity.
It is preferable in this configuration that the mixing ratio of the terbium activated rare earth borate green phosphor to the whole composition in the mixed phosphor is 10 to 75 weight %.